Lattice deformation from interaction with electrons heated by an ultrashort laser pulse

We propose a model describing the destruction of metals under ultrashort intense laser pulses when heated electrons affect the lattice through the direct electron-phonon interaction. The metal consists of hot electrons and a cool lattice. The lattice deformation is estimated immediately after the laser pulse up to the electron temperature relaxation time. The hot electrons are described with help of the Boltzmann and heat conduction equations. We use an equation of motion for the lattice displacements with the electron force included. Estimates of the lattice deformation show that the ablation regime can be achieved. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 195–199 (10 August 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Gate-tunable bandgap in bilayer graphene

The tight-binding model of bilayer graphene is used to find the gap between the conduction and valence bands as a function of both the gate voltage and the doping level by donors or acceptors. The total Hartree energy is minimized and an equation for the gap is obtained. This equation for the ratio of the gap to the chemical potential is determined only by the screening constant. Therefore, the gap is strictly proportional to the gate voltage or the carrier concentration in the absence of donors or acceptors. But in the case where the donors or acceptors are present, the gap demonstrates an asymmetric behavior on the electron and hole sides of the gate bias. A comparison with experimental data obtained by Kuzmenko et al. demonstrates a good agreement.     

Transport phenomena at metal surfaces

Previous theoretical treatments of the scattering of conduction electrons at surfaces are reviewed and it is found that a more complete theory is necessary if the effects of surface scattering in transport phenomena are to be adequately understood. The boundary condition for the distribution function is derived and analysed in terms of the angle-dependent scattering probability. The skin effect, cyclotron resonance and the resistance of thin films and wires are considered in detail.     

Plasma torches and electrophysical parameters of the diaphragm discharge in water

This work is aimed at studying plasma torch formation, voltages, currents, power distribution, and resistance variation in the case of the little understood low-energy (≤10 J) diaphragm discharge initiated in water and salt solutions. Plasma torches associated with this type of discharge differ considerably from those of other discharges. Different shapes of anode and cathode torches, breakdowns between the diaphragm and one of the electrodes, and a specific form of cathode breakdown are observed. It is found that the electrical conductivity of the medium influences the parameters of the plasma formations, current pulses, dielectric strength of the medium, current pulse variation at “semibreakdowns,” etc. Based on the experimental data, it is concluded that the process of discharge initiation differs from that described in the literature.     

Optical properties of doped graphene layers

The reflectance of a graphene monolayer, as well as of a system of monolayers, is calculated in the infrared range. A quantum expression for the conductivity in the collisionless regime that depends on the frequency, the temperature, and the concentration of carriers is used in the calculations. Above the threshold of the interband electron absorption, the reflectance decreases with increasing frequency. With decreasing temperature, excitation of plasmons in the system of layers is possible in a narrow range near the threshold, which results in the occurrence of a deep and sharp minimum in the frequency dependence of the reflectance.     

Perturbation theory for a hamiltonian linear in quasimomentum

Perturbation theory has been proposed to take into account small terms in the multiband Hamiltonian, which lead to significant changes such as the trigonal warping of the Fermi surface. The theory is similar to the “cross technique” and is reduced to the self-energy corrections to the matrix Green’s function. A particular application to graphite and a graphene bilayer has been given.     

Infrared absorption and Raman scattering on coupled plasmon-phonon modes in superlattices

We theoretically consider a superlattice formed by thin conducting layers spatially separated between insulating layers. The dispersion of two coupled phonon-plasmon modes of the system is analyzed by using the Maxwell equations, with the retardation effect included. Both transmission for the finite plate and the absorption for the semi-infinite superlattice in the infrared are calculated. Reflectance minima are determined by the longitudinal and transverse phonon frequencies in the insulating layers and by the density-state singularities of the coupled modes. We also evaluate the Raman cross section from the semi-infinite superlattice. The text was submitted by the authors in English.     

Thermodynamics of electron-hole liquids in graphene

The impact of Coulomb interactions on the chemical potential, heat capacity, and oscillating magnetic moment is studied. The cases of low and high temperatures are considered. At low temperatures, doped graphene behaves as the common Fermi liquids with the power temperature laws for thermodynamic properties. However, at high temperatures and relatively low carrier concentrations, it exhibits the collective electron-hole behavior: the chemical potential tends to its value in the undoped case going with the temperature to the charge neutrality point. Simultaneously, the electron contribution into the heat capacity tends to the constant value as in the case of the Boltzmann statistics.